Thermoelectric cooling of vidicons



Mal'Ch 24 1964 s. l.. BENDELL THERMOELECTRIC COOLING oF vIDIcoNs FiledMarch 27, 1962 United States Patent O 3,125,498 THERMGELECTRIC COOLING FVIDECNS Sidney L. Rendell, Haddon Heights, NJ., assigner to RadioCorporation of America, a corporation oi' Delaware Filed Mar. 27, 1962,`Ser. No. 1S2,860 Claims. (Cl. 315-8) The invention relates to improvedtelevision cameras lthat include a picture pickup tube of the typehaving a photoconductive target or screen, a vidicon being an example ofa tube of this type. The invention relates particularly tothermoeleotnic cooling of pickup tubes of this 'type and to means forpreventing the cooling current from skewing or otherwise adverselyaecting the transmitted picture.

The invention will be described, by Way of example, as it may be appliedto the television color camera described in application S.N. 119,871,tiled lune 27, 1961, in the name of A. V. Bedford and entitled ColorTelevision Camera System. This television camera comprises three colorpickup tubes of the vidicon tube and' one high resolution pickup tubesuch -as an image orthicon which functions as a luminance pickup tube.It is desirable to cool the vidicon target both to improve the vidiconsensitivity and to prevent wide variations in the temperature of thevidicon target. The latter is of interest because the vidicon darkcurrent increases with an increase in target temperature.

In practicing the present invention the cooling is done by use of athermoelectric cooling unit, and the axial component of the magneticfield produced by the cooling unit current is balanced out by providinga bucking or cancelling axial ield. Much of the magnetic iield producedby the flow of current through the cooling unit is transverse to thelongitudinal axis of the vidicon and can be prevented from Vreaching thevidicon by means of shielding. It is found, however, that there is amagnetic field component that is coaxial with the vidicon which is ofsuiiicient strength to atleet the vidicon detiection and skew thetransmitted picture unless it is prevented from reaching the vidicon.

The invention will be described in detail with reference to theaccompanying drawing, in which:

FIGURE 1 is a plan view, partly in section, illustrating one embodimentof the invention,

FlGURE 2 is a view in cross section taken on the line 2-2 of FIGURE 1,

FIGURE 3 is a plan view of a thermoelectric cooling unit that isincluded in the apparatus of -FIGURE l, and

'FIGURE 4 is view in cross section taken on the line 4-4 of IFIGURE 3,together with a -showing of a iield balancing coil and circuitconnections as employed in the apparatus of FIGURE 1.

In the several figures similar parts are indicated by like referencecharacters.

Referring to FIGS. l and 2, the three vidicons of the color camera aresupported in =a comparatively deep rectangular box 11 that is of mumetal for shielding purposes. Only one vidicon with its cooling means,axial iield cancellation means, and optical system is shown, the othertwo vidicons being positioned beneath the one shown in FIG. 1 and beingcooled and protected from magnetic iields in the same way. The followingdescription applies to all three vidicons.

A metal plate 12 is attached to the side of the box 11. 'Ihe base plateserves to support the various elements, and also serves as a heat sink.

The face plate end of the vidicon is supported in lirm abutting relationto Ia block of copper 13 which is cooled by a thermoelectric coolingunit 14. Thus the face plate and the photoconductive target locatedclose thereto are ICC cooled. The cooling unit 14 is in close contactwith the base plate 12. The copper block 13 may be supported from thebase plate 12 with the cooling unit 14 clamped between the block 13 `andthe `base plate 12. The cross section view of the cooling unit 14 inFIG. 1 is taken on the line 1-1 of FIG. 4.

In order to hold the face plate end of the vidicon in position, aring-like member 16 of nylon is supported on the small end of the copperblock 13. A portion of member 16 extend-ing beyond the block 13 isshaped to receive the end of the vidicon in a snug fit therebysupporting the end of the vidicon. The other end of the vidicon issupported by a tube socket 17 which in turn is supported by aninsulating support 18 secured to the base plate 12.

The vidicon is surrounded by a cylindrical shield 19 of ferrite. Thisshield is supported by metal supports 21 and 22 which Iare secured tothe base plate 12.

A camera lens 23 is positioned in front of the vidicon for imaging thescene lto be transmitted on the vidicon target. The lens is supported byan insulating support 24 which is secured to the base plate 12. Thecamera lenses for the other two vidicons are indicated at 2.3 in FIG. 2.The supports for these lenses are indicated at 24.

The mirror 26 for reflecting one of the primary colors of the scene tothe camera lens is supported by the base plate 12, and is adjusted to beat an angle of 45 degrees to the vertical.

A heat exchanger 27 containing cooling tins 30 is secured in closecontact with the base plate 12 to remove heat from the hot side of thecooling unit 14. A blower 2.8 forces air through the heat exchanger.

The heavy flow of direct current through cooling unit 14 produces amagnetic tield that should not reach the vidicon. The component of thisield transverse to the longitudinal axis of the vidicon does not disturbthe vidicon because it is shielded by the ferrite shield 19. The axialcomponent of this iield can-not be prevented from reaching the vidiconby the use of shielding, however, s-ince there must be a clear opticalpath for the scene to be imaged on the orthicon target. The problem issolved by providing a balancing iield that bucks out the axial field.This balancing field is provided, in the specific example illustrated,by a balancing coil 31 comprising two turns of wire, that are connectedin series with the cooling unit so that the cooling current flowsthrough the coil. The balancing coil 31 is of sutiicient diameter and isso positioned that it does not interfere with the optical path of thescene being televised. In the example illustrated, the two turns arewound around the lens mounting structure. They are wound in thedirection to provide a magnetic field that opposes the undesired axialmagnetic iield of the cooling unit.

The cooling unit and cancellation of its yaxial iield will be discussedfurther, but at this point attention is directed to the optics chamberlocated Ibetween the camera lens and the vidicon. It will be noted thatit is conical in shape, being formed by a conical opening in the coppercooling block 13. The chamber is both light proof and dust proof, thisbeing insured by the use of suit-able thermal insulation 32 such asurethane which seals the joints.

Refer now to the thremoelectric cooling unit shown in plan view in FIG.3 and in section in FIG. 4, the section being taken on the line 4 4 ofFIG. 3 looking in the direction of the arrows. In the sectional view ofFIG. 4 the foamed-in-place insulation of the cooling unit is omitted forthe purpose of showing the structure. The cooling unit illustrated is ofa well known type comprising P type and N type materials (FIG. 4) whichare connected in series relation by means of copper plates 33a, 33h,etc. on the hot side of the unit and by means of copper plates 33A, etc.on the cold side of the unit. Only the first copper plate 33A and thelast copper plate 33H on the cold side are shown.

In the example illustrated, the cooling current, about 2O amperes inthis example, flows from plate 33a, down a P type element to plate 33Athrough plate 33A and up an N type element to plate 33h, through plate33h and down a P type element to plate 33B (not shown), etc., until thefinal copper plate 331' is reached. The direction of the current flowwill be understood from the foregoing description and from an inspectionof FIG. 3 where the arrows on the copper plates indicate the directionof current ow. One result of this current flow is the production of amagnetic eld having a component that is eoaxial with the vidicon aspreviously stated. The coil 31 for bucking out this axial field is shownin FIG. 4 connected in series with the cooling unit. If the coolingcurrent is increased either manually or automatically (as by means of a.thermostatic control), this causes the eld bucking current owing throughcoil 31 to be increased by the same amount. Thus, there results astronger bucking eld which balances out the increased axial eldcomponent due to the increased cooling current.

What is claimed is:

1. A picture pickup tube of the type having a photoconductive targetclose to the end or face plate of the tube; means for cooling saidtarget, said means comprising a metal cooling block in Contact with saidface plate, said cooling block having an opening therethrough which iscoaxial with said tube for providing an optical path through which animage may be formed on said target, a thermoelectric cooling unit incontact with said cooling block; a magnetic eld balancing coilpositioned opposite the face plate of said tube and positioned coaxiallywith said tube, and means connecting said coil and said cooling unit inseries, said coil being wound in the direction to provide a eld thatopposes the axial component of the magnetic eld caused by the current owthrough the cooling unit, said coil also having a number of turns suchthat its ield balances out said axial component.

2. A picture pickup tube of the type having a photoconductive targetclose to the end or face plate of the tube; means for cooling saidtarget, said means comprising a metal cooling block in contact with saidface plate, said cooling block having an opening therethrough which iscoaxial with said tube for providing an optical path through which animage may be formed on said target, a thermoelectric cooling unit incontact with said cooling block; a magnetic iield balancing coilpositioned opposite the face plate of said tube and positioned coaxiallywith said tube, means connecting said coil and said cooling unit inseries whereby the cooling current flows through both said coil and saidcooling unit, said coil being wound in the direction to provide a eldthat opposes the axial component of the magnetic field caused by thecurrent iiow through the cooling unit, said coil also having a number ofturns such that its field balances out said axial component, andelectromagnetic shielding means surrounding said tube for shielding itfrom the transverse component of said magnetic eld.

3. In combination, a vidicon having a face plate at one end and aphotoconductive target close to said face plate, a cooling bloclt ofgood thermal conductivity positioned with one end in contact with saidface plate, said cooling block having an opening therethrough that iscoaxial with said vidicon for providing an unobstructed optical path, acamera lens positioned at the other end of said cooling block with theoptical axis of the lens coaxial with the vidicon, a thermoelectriccooling unit positioned against said cooling block for cooling it whencooling current tiows through said cooling unit, said cooling currentproducing an undesired axial magnetic iield component, and means forproducing a balnacing magnetic field to balance out said axialcomponent.

4. In combination, a vidicon having a face plate at one end and aphotoconductive target close to said face plate, a cooling block of goodthermal conductivity positioned With one end in contact with said faceplate, said cooling block having an opening therethrough that is coaxialwith said vidicon for providing an unobstructed optical path, a cameralens which has the lens elements in a lens mounting structure that ispositioned at the other end of said cooling block with the optical axisof the lens coaxial with the vidicon, a thermoelectric cooling unitpositioned against said cooling block for cooling it when coolingcurrent ows through said cooling unit, said cooling current producing anundesired axial magnetic eld component, and means for producing abalancing magnetic field to balance out said axial component, said lastmeans cornprising a coil wound around the lens mounting structure.

5. In combination, a vidicon having a face plate at one end and aphotoconductive target close to said face plate, a cooling block of goodthermal conductivity positioned with one end in contact with said faceplate, said cooling block having an opening therethrough that is coaxialwith said vidicon for providing an unobstructed optical path, a cameralens which has the lens elements in a lens mounting structure that ispositioned at the other end of said cooling block with the optical axisof the lens coaxial with the vidicon, a thermoelectric cooling unitpositioned against said cooling block for cooling it when coolingcurrent flows through said cooling unit, said cooling current producingan undesired axial magnetic field component, and means for producing abalancing magnetic field to balance out said axial component, said lastmeans comprising a coil wound around the lens mounting structure andconnected in series with said cooling unit.

References Cited in the tile of this patent UNITED STATES PATENTS2,517,807 Sziklai Aug. 8, 1950 2,879,424 Garbuny et al. Mar. 24, 19592,907,914 Brownell Oct. 6, 1959 2,967,961 Heil Jan. 10, 1961 2,975,283Morton Mar. 14, 1961 3,064,440 Waller Nov. 20, 1962

1. A PICTURE PICKUP TUBE OF THE TYPE HAVING A PHOTOCONDUCTIVE TARGETCLOSE TO THE END OR FACE PLATE OF THE TUBE; MEANS FOR COOLING SAIDTARGET, SAID MEANS COMPRISING A METAL COOLING BLOCK IN CONTACT WITH SAIDFACE PLATE, SAID COOLING BLOCK HAVING AN OPENING THERETHROUGH WHICH ISCOAXIAL WITH SAID TUBE FOR PROVIDING AN OPTICAL PATH THROUGH WHICH ANIMAGE MAY BE FORMED ON SAID TARGET, A THERMOELECTRIC COOLING UNIT INCONTACT WITH SAID COOLING BLOCK; A MAGNETIC FIELD BALANCING COILPOSITIONED OPPOSIT THE FACE PLATE OF SAID TUBE AND POSITIONED COAXIALLYWITH SAID TUBE, AND MEANS CONNECTING SAID COIL AND SAID COOLING UNIT INSERIES, SAID COIL BEING WOUND IN THE DIRECTION TO PROVIDE A FIELD THATOPPOSES THE AXIAL COMPONENT OF THE MAGNETIC FIELD CAUSED BY THE CURRENTFLOW THROUGH THE COOLING UNIT, SAID COIL ALSO HAVING A NUMBER OF TURNSSUCH THAT ITS FIELD BALANCES OUT SAID AXIAL COMPONENT.